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Publication numberUS7022655 B2
Publication typeGrant
Application numberUS 10/454,109
Publication dateApr 4, 2006
Filing dateJun 4, 2003
Priority dateNov 15, 2002
Fee statusLapsed
Also published asUS6624127, US20040097388
Publication number10454109, 454109, US 7022655 B2, US 7022655B2, US-B2-7022655, US7022655 B2, US7022655B2
InventorsJustin K. Brask, Robert B. Turkot, Jr., Vijayakumar S. Ramachandrarao
Original AssigneeIntel Corporation
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Using supercritical carbon dioxide; removal etching residues
US 7022655 B2
Supercritical carbon dioxide may be utilized to remove resistant residues such as those residues left when etching dielectrics in fluorine-based plasma gases. The supercritical carbon dioxide may include an ionic liquid in one embodiment.
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1. A cleaning material comprising:
supercritical carbon dioxide;
an ionic liquid; and
a co-solvent including fluorine substituents.
2. The material of claim 1 wherein said ionic liquid is only partially miscible in supercritical carbon dioxide.
3. The material of claim 1 wherein said ionic liquid is fully miscible in supercritical carbon dioxide.
4. The material of claim 2 or 3 wherein said ionic liquid includes an imidazolium compound.
5. The material of claim 4 wherein said compound is 1-butyl-3-methylimidazolium hexafluorophosphate.

This application is a Divisional of U.S. application Ser. No. 10/295,150, filed Nov. 15, 2002, now U.S. Pat. No. 6,624,127.


This invention relates generally to processes for manufacturing semiconductor integrated circuits and, particularly, to the removal of etch residues.

Fluorine-based plasma etching is commonly used to etch photoresist to generate patterns on a semiconductor device. A residue is left behind on the etched wafer that essentially includes constituents of the plasma gas and the material etched. Normally, gases composed of carbon and fluorine are used for plasma etching resulting in a residue containing carbon and fluorine. Further, the residue may be polymerized due to the generation of free radicals and ions in the high-energy plasma environment.

With photoresists in advanced semiconductor processes, such as the 193 nm photoresist, wherein a fluorine-rich plasma etch is used, and with 157 nm, wherein the photoresist itself is fluorine-based the etch residue may be difficult to remove. This residue may include carbon, hydrogen, and fluorine, and is highly chemically inert and is, therefore, relatively difficult to remove with conventional wet chemical etches. The use of delicate interlayer dielectrics, including porous materials, may prevent the use of ashing for residue removal. Conventional wet cleans may not work well with this relatively inert chemical residue. Few liquid solvents can penetrate fluorine-based polymers like teflon.

Thus, there is a need for a better way to remove resistant etch residues.


Supercritical carbon dioxide has gas-like diffusivity and viscosity and liquid-like densities, while being almost chemically inert. Hence a host of chemically reactive agents may almost always be used in conjunction during supercritical carbon dioxide-based cleans. Carbon dioxide becomes supercritical at temperatures above 30 C. and pressures above 1000 pounds per square inch. A fluid is considered to be supercritical when its pressure and temperature are above the critical values.

A variety of chemically reactive agents are soluble in supercritical carbon dioxide, such as the solvents dimethyl acetamide (DMAC), sulfolane, organic peroxides, ethers, glycols, organic bases, and strong organic and mineral acids, to mention a few examples. The higher degree of swelling of the fluorine-based residue by fluorocarbons dissolved in supercritical carbon dioxide and increased diffusion of supercritical carbon dioxide and the dissolved reagents therein (fluorocarbons and the other chemical reagents) may enhance residue deterioration and removal. A high flow rate of supercritical carbon dioxide may lend the ability to use highly reactive chemicals as opposed to conventional wet chemistries, which have a long contact time with the dielectric material.

Ionic liquids are salts that exist in liquid form at temperatures from 10 to 200 C. Ionic liquids have a positive and negative charge. They exhibit low viscosity and no measurable vapor pressure. Ionic liquid can dissolve a range of organic, inorganic, and polymeric materials at high concentrations. Generally, ionic liquids are non-corrosive. Examples of ionic liquids include salts of alkylmethylimidazolium.

A member from the imidazolium family of ionic liquids may be combined with supercritical carbon dioxide to increase variability and polarity and hence selectivity for various cleaning applications. The ionic liquid may be mixed into supercritical carbon dioxide in a way that the ionic liquid is fully, or only partially, miscible in the carbon dioxide medium, depending on the application.

By mixing ionic liquids with supercritical carbon dioxide, clean chemistries with high polar variability may be achieved. For example, derivatives of 1-butyl-3-methylimidazolium hexafluorophosphate may be used which are partially miscible with supercritical carbon dioxide.

The addition of highly polar ionic liquids in various stoichiometries to supercritical carbon dioxide provides a broader range of tunable polarities, enabling variation and selectivity for material cleaning. Moreover, such liquids have effectively zero vapor pressure and, therefore, they can be recycled upon heating. The particles and solutes are degraded and then can be filtered or separated off. In addition, other ionic liquids may also be used with supercritical carbon dioxide. One may pick and choose among the various available ionic pairs to make a liquid that fits a particular need such as dissolving certain chemicals in a reaction or extracting specific molecules from solution.

Supercritical carbon dioxide may be forced through a solution containing the undesired material and an ionic liquid. The carbon dioxide in its supercritical state may be near room temperature but is highly pressurized. The supercritical carbon dioxide may have a liquid consistency yet, like a gas, expands to fill the available space. When droplets of supercritical carbon dioxide are forced through an ionic liquid, the carbon dioxide can pull impurities out of the ionic liquid while leaving the ionic liquid unchanged. Carbon dioxide is sufficiently soluble in 1-butyl-3-methylimidazolium hexafluorophosphate to reach a mole fraction of 0.6 at 8 MPa. Blanchard, Lynette A. et al., Nature, 399, 2829 (1999).

Dissolved fluorocarbons or other reagents in supercritical carbon dioxide may be quickly transported into residues left after fluorine-based etches of photoresist due to the high diffusivity of supercritical carbon dioxide and, particularly, the diffusivity of supercritical carbon dioxide in polymers and small molecules in polymers swollen by supercritical carbon dioxide. Since the fluorocarbons are chemically similar to the etch residue, the etch residue swells. This further increases the access of the supercritical carbon dioxide into the interior of the etch-residue and weakens the residue. The fluorocarbon also breaks into the hard crust of the residue, which the supercritical carbon dioxide by itself may be unable to enter and swell, to introduce the reactive agents into the residue. Addition of an ionic liquid to the above supercritical carbon dioxide/fluorocarbon mixture allows for polar variability/tunibility of said mixture.

While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US6579343 *Apr 1, 2002Jun 17, 2003University Of Notre Dame Du LacContacting gas with a liquid ionic compound comprising a nitrogen-containing heterocyclic cation
US6624127 *Nov 15, 2002Sep 23, 2003Intel CorporationHighly polar cleans for removal of residues from semiconductor structures
US20030085156 *Nov 6, 2002May 8, 2003Schoonover Roger E.Method for extraction of organosulfur compounds from hydrocarbons using ionic liquids
US20040097388 *Jun 4, 2003May 20, 2004Brask Justin K.Using supercritical carbon dioxide; removal etching residues
DE10123467A1 *May 15, 2001Nov 21, 2002Studiengesellschaft Kohle MbhActivation of cationic transition metal catalyst, useful in e.g. metathesis, oligomerization reaction, involves using ionic liquid and compressed carbon dioxide
Non-Patent Citations
1 *"Green Processing Using Ionic Liquids and CO2", Nature, vol. 399, May 6, 1999, Macmillan Magazine Ltd., pp. 28, 29.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7553803 *Mar 1, 2004Jun 30, 2009Advanced Technology Materials, Inc.Removing silicon-containing particulate material from surface of semiconductor wafer using supercritical fluid, at least one co-solvent, at least one etchant species, at least one surface passivator, a binder interactive with silicon-containing particulate material, deionized water, surfactant
US7585415Jun 17, 2005Sep 8, 2009Matheson Tri-GasFluid storage and purification method and system
US7638058 *Apr 7, 2005Dec 29, 2009Matheson Tri-Gasstoring and dispensing a fluid includes providing a vessel configured for selective dispensing of the fluid therefrom; The fluid is contacted with the ionic liquid for take-up of the fluid by the ionic liquid
US7670490Jun 17, 2005Mar 2, 2010Matheson Tri-Gas, Inc.Fluid storage and purification method and system
US7896954Sep 1, 2009Mar 1, 2011Matheson Tri-Gas, Inc.Fluid storage and purification method and system
US7938968Mar 18, 2008May 10, 2011Matheson Tri Gasstoring and dispensing a fluid includes providing a vessel configured for selective dispensing of the fluid therefrom. The vessel contains an ionic liquid therein. The fluid is contacted with the ionic liquid for take-up of the fluid by the ionic liquid.
US8083945Mar 2, 2010Dec 27, 2011Matheson Tri-Gas, Inc.Fluid storage and purification method and system
US8153533Sep 24, 2008Apr 10, 2012Lam ResearchMethods and systems for preventing feature collapse during microelectronic topography fabrication
U.S. Classification510/175, 510/407
International ClassificationC11D7/50, C11D11/00, C11D7/32, C11D7/36
Cooperative ClassificationC11D7/36, C11D7/3281, C11D11/0047
European ClassificationC11D7/36, C11D7/32K, C11D11/00B2D8
Legal Events
May 27, 2014FPExpired due to failure to pay maintenance fee
Effective date: 20140404
Apr 4, 2014LAPSLapse for failure to pay maintenance fees
Nov 15, 2013REMIMaintenance fee reminder mailed
Sep 30, 2009FPAYFee payment
Year of fee payment: 4